The law about foraging can vary greatly, depending on your location. Search online for "foraging law" plus your location. Please note that special rules may apply to parks.

British Countryside Code (applies elsewhere too)

• Be safe - plan ahead and follow any signs
• Leave gates and property as you find them
• Protect plants and animals and take your litter home
• Keep dogs under close control
• Consider other people

That tempting lush meadow full of wild flowers may be a hay or silage field. Walking through the tall vegetation will flatten it, and make it unavailable for harvest.

Except in times of need

• pick only plants which grow in profusion or are considered weeds.
• avoid digging up roots which effectively destroys the plant.
• avoid picking flowers; they give little sustenance to humans but are food to many insects, and are needed by annuals to set seed for the plant's survival. Where this is not an issue, it may still be better to allow the flower to develop fruit or edible seeds, where this is of greater food value.
• avoid stripping a plant of leaves; pick a few from a larger number of plants
• leave some fruit or nuts for wildlife, especially close to the ground for mammals, or on higher branches for birds
• gather in moderation; there may also be others who forage in the same location
• avoid very small or young plants; many plants need to be gathered for a meal
• tread lightly, literally, to avoid damaging plants or the delicate mycelium of fungi
• bark should only be removed from trees which are to be felled; never ring-bark a living tree
• The countryside is best enjoyed quietly, not just by people, but also by wildlife, especially during the breeding season.

• scissors
• flat based basket
• paper bags
• belt pouch
• rubber or leather gloves for picking nettles
• hooked stick